Method for polishing silicon wafer with reduced wear on carrier, and polishing liquid used therein

ABSTRACT

Provided is a method that is for polishing a silicon wafer by a polishing device using a carrier holding the silicon wafer, and that can reduce wear on the carrier. In this polishing method, a polishing liquid used in the polishing device contains 0.1-5 mass %, in terms of the concentration of silica, silica particles comprising: silica particles (A) having an average primary particle size of 4-30 nm as measured by BET, and having an (X2/X1) ratio of 1.2-1.8, where X2 (nm) represents an average particle size along the major axis thereof as calculated from a perspective projection image obtained using an electron beam, and X1 (nm) represents the average primary particle size as measured by BET; and silica particles (B) having an average primary particle size of more than 30 nm but not more than 50 nm as measured by BET, and having a (X2/X1) ratio of 1.2-1.8, where X2 (nm) represents an average particle size along the major axis thereof as calculated from a perspective projection image obtained using an electron beam, and X1 (nm) represents the average primary particle size as measured by BET, wherein the mass ratio of the silica particles (A) to the silica particles (B) is 100:0 to 85:15.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of co-pending applicationSer. No. 17/279,482, filed on Mar. 24, 2021, which is the National Phaseunder 35 U.S.C. § 371 of International Application No.PCT/JP2019/036908, filed on Sep. 20, 2019, which claims the benefitunder 35 U.S.C. § 119(a) to Patent Application No. 2018-179508, filed inJapan on Sep. 25, 2018, all of which are hereby expressly incorporatedby reference into the present application.

TECHNICAL FIELD

The present invention relates to a method for polishing a silicon waferwith a polishing machine using a carrier holding the silicon wafer. Inparticular, the present invention relates to a method for polishing asilicon wafer with a double-sided polishing carrier used in adouble-sided polishing machine for polishing a silicon wafer.

BACKGROUND ART

The polishing of a silicon wafer is used in each process including awrapping process and a polishing process.

Examples of a polishing machine include a single-sided polishing machineand a double-sided polishing machine, and when polishing the siliconwafer using a carrier, the double-sided polishing machine is mainlyused. The double-sided polishing machine can process many silicon wafersat the same time by a processing method referred to as a batchtreatment.

The double-sided polishing machine has a structure, wherein a lowersurface plate and an upper surface plate, and a plurality of carriers inbetween them drive to rotate and its rotation is performed planetarilyalong a gear. The carrier has a disk-shaped structure that has a gear onthe outer edge and can insert a silicon wafer, and in some cases, aplurality of silicon wafers can be inserted into one carrier. In thedouble-sided polishing machine, these carriers receive the supply of apolishing liquid between a lower grindstone and an upper grindstone, andboth sides of a silicon wafer are polished while planetarily rotating.

The carrier exists while being pressurized between the lower surfaceplate and the upper surface plate, which a polishing pad is attached to,and is constantly exposed to a polishing state with the polishingliquid, so that the carrier itself is worn together with a siliconwafer.

The carrier is replaced with a new carrier when polishing wear issevere, but the carrier itself is constantly exposed to polishing duringthe polishing process, and the carrier itself is polished, so thatdeterioration of polishing accuracy (specifically, evenness, flatness,roughness, parallelism/thickness variation, etc.) due to a deformationof the carrier itself, variation in polishing rate (i.e., polishingamount per unit time) and polishing quality, and noise (i.e., abnormalnoise) generated from the carrier have become problems.

Patent Literature 1 discloses a carrier in which the surface of acarrier is coated with a hard material selected from the groupconsisting of polyvinylidene fluoride, polyamide, polypropylene,polyethylene, polyethylene terephthalate, polycarbonate, polystyrene,and a polymer alloy thereof as a carrier used in a lapping device, apolishing machine, and a grinding device to maintain low wear on thecarrier.

Patent Literature 2 discloses a method for polishing a silicon wafer ina method of producing an epitaxial wafer in which an epitaxial layer isgrown using a vapor phase growth device after the polishing is performedwith a double-sided polishing machine including a carrier.

CITATION LIST Patent Literature

-   PATENT LITERATURE 1: JP 2009-099980 A-   PATENT LITERATURE 2: JP 2016-204187 A

SUMMARY OF INVENTION Technical Problems

An object of the present invention is to provide a novel polishingmethod to make wear on a carrier reduced in a method for polishing asilicon wafer with a polishing machine using the carrier to hold thesilicon wafer. Also, it is another object of the present invention toprovide a polishing liquid used in the method.

Solution to Problems

Specifically, various aspects of the present invention are as follows.

[Aspect 1] A method for polishing a silicon wafer with a polishingmachine using a carrier to hold the silicon wafer,

-   -   wherein a polishing liquid used in the polishing machine        comprises silica particles at a silica concentration of 0.1% by        mass to 5% by mass,        -   the silica particles consisting of:            -   silica particles (A) having an average primary particle                size of 4 nm to 30 nm as measured by BET method, and                having a ratio (X2/X1) of 1.2 to 1.8 when representing a                major-axis average particle size calculated from                projection images by transmission electron microscope as                (X2) nm and an average primary particle size as measured                by the BET method as (X1) nm; and            -   silica particles (B) having an average primary particle                size of more than 30 nm and 50 nm or less as measured by                the BET method, and having a ratio (X2/X1) of 1.2 to 1.8                when representing a major-axis average particle size                calculated from projection images by transmission                electron microscope as (X2) nm and an average primary                particle size as measured by the BET method as (X1) nm,            -   wherein a mass ratio of the silica particles (A) to the                silica particles (B) is 100:0 to 85:15.

[Aspect 2] A method for polishing a silicon wafer with a polishingmachine using a carrier to hold the silicon wafer,

-   -   wherein a polishing liquid used in the polishing machine        comprises:    -   silica particles at a silica concentration of 0.1% by mass to 5%        by mass, the silica particles consisting of: silica        particles (A) having an average primary particle size of 4 nm to        30 nm as measured by BET method; and silica particles (B) having        an average primary particle size of more than 30 nm and 50 nm or        less as measured by the BET method, wherein a mass ratio of the        silica    -   particles (A) to the silica particles (B) is 100:0 to 85:15; or        silica particles at a silica concentration of 0.1% by mass or        more and less than 2.5% by mass, the silica particles consisting        only of silica particles (B′) having an average primary particle        size of more than 30 nm and less than 45 nm as measured by the        BET method.

[Aspect 3] The method according to [Aspect 2], wherein the silicaparticles (A), the silica particles (B), and the silica particles (B′)have, when representing a major-axis average particle size calculatedfrom projection images by transmission electron microscope as (X2) nmand an average primary particle size as measured by the BET method as(X1) nm, a ratio (X2/X1) of 1.2 to 1.8.

[Aspect 4] The method according to any one of any one of [Aspect 1] to[Aspect 3] using a double-sided polishing machine as the polishingmachine, comprising polishing the silicon wafer under conditions of aload of 30 to 1000 g/cm², a lower surface plate rotation speed of 5 to100 rpm, an upper surface plate rotation speed of 2 to 30 rpm, arotation ratio of a lower surface plate/an upper surface plate of 1 to10, a polishing time of 10 minutes to 3 hours, and a polishing liquidsupply amount of 1 to 20 liters/minute.

[Aspect 5] The method according to any one of [Aspect 1] to [Aspect 4],wherein the carrier is an epoxy glass carrier.

[Aspect 6] The method according to any one of [Aspect 1] to [Aspect 5],wherein the polishing liquid further comprises at least one additiveagent selected from the group consisting of an alkaline component, awater-soluble compound, and a chelating agent.

[Aspect 7] The method according to [Aspect 6], wherein the alkalinecomponent is sodium hydroxide, potassium hydroxide, ammonia, primaryammonium hydroxide, secondary ammonium hydroxide, tertiary ammoniumhydroxide, quaternary ammonium hydroxide, lithium carbonate, sodiumcarbonate, potassium carbonate, lithium hydrogen carbonate, sodiumhydrogen carbonate, potassium hydrogen carbonate, sodium hydroxide, orpotassium hydroxide.

[Aspect 8] The method according to [Aspect 6], wherein the chelatingagent is an aminocarboxylic acid-based chelating agent or a phosphonicacid-based chelating agent.

[Aspect 9] The method according to any one of claims [Aspect 1] to[Aspect 8], wherein a pH value of the polishing liquid is 7 to 12.

[Aspect 10] A polishing liquid for a polishing machine using a carrierto hold a silicon wafer,

-   -   the polishing liquid comprising silica particles at a silica        concentration of 0.1% by mass to 5% by mass,        -   the silica particles consisting of:            -   silica particles (A) having an average primary particle                size of 4 nm to 30 nm as measured by BET method, and                having a ratio (X2/X1) of 1.2 to 1.8 when representing a                major-axis average particle size calculated from                projection images by transmission electron microscope as                (X2) nm and an average primary particle size as measured                by the BET method as (X1) nm; and            -   silica particles (B) having an average primary particle                size of more than 30 nm and 50 nm or less as measured by                the BET method, and having a ratio (X2/X1) of 1.2 to 1.8                when representing a major-axis average particle size                calculated from projection images by transmission                electron microscope as (X2) nm and an average primary                particle size as measured by the BET method as (X1) nm,            -   wherein a mass ratio of the silica particles (A) to the                silica particles (B) is 100:0 to 85:15.

[Aspect 11] A polishing liquid for a polishing machine using a carrierto hold a silicon wafer,

-   -   the polishing liquid comprising:    -   silica particles at a silica concentration of 0.1% by mass to 5%        by mass, the silica particles consisting of: silica        particles (A) having an average primary particle size of 4 nm to        30 nm as measured by BET method, and silica particles (B) having        an average primary particle size of more than 30 nm and 50 nm or        less as measured by the BET method, wherein a mass ratio of the        silica particles (A) to the silica particles (B) is 100:0 to        85:15; or    -   silica particles at a silica concentration of 0.1% by mass or        more and less than 2.5% by mass, the silica particles consisting        only of silica particles (B′) having an average primary particle        size of more than 30 nm and less than 45 nm as measured by the        BET method.

[Aspect 12] The polishing liquid according to [Aspect 11], wherein thesilica particles (A), the silica particles (B), and (B′) have, whenrepresenting a major-axis average particle size calculated fromprojection images by transmission electron microscope as (X2) nm and anaverage primary particle size as measured by the BET method as (X1) nm,a ratio (X2/X1) of 1.2 to 1.8.

Advantageous Effects of Invention

A double-sided polishing machine has a structure, wherein a lowersurface plate and an upper surface plate, and a plurality of carriers inbetween them drive to rotate, and its rotation is performed planetarilyalong a gear. The carrier has a disk-shaped structure that has a gear onthe outer edge and can insert a silicon wafer, and in some cases, aplurality of silicon wafers can be inserted into one carrier. In thedouble-sided polishing machine, their carriers receive the supply of apolishing liquid between a lower grindstone and an upper grindstone, andboth sides of a silicon wafer are polished while planetarily rotating.

The carrier exists while being pressurized between the lower surfaceplate and the upper surface plate, which a polishing pad is attached to,and is constantly exposed to a polishing state with the polishingliquid, so that the carrier itself is worn together with a siliconwafer.

The carrier is replaced with a new carrier when the polishing wear issevere, but the carrier itself is constantly exposed to polishing duringthe polishing process, and the carrier itself is polished, so thatdeterioration of polishing accuracy (specifically, evenness, flatness,roughness, parallelism/thickness variation, etc.) due to a deformationof the carrier itself, variation in polishing rate and polishingquality, and noise generated from the carrier have become problems.

According to the method for polishing a silicon wafer according to thepresent invention and the polishing liquid according to the presentinvention, when polishing the silicon wafer with a polishing machineusing a carrier to hold the silicon wafer, the amount of wear on thecarrier exposed to the polishing together with the silicon wafer can bereduced while maintaining a good polishing rate for polishing thesilicon wafer. When a silicon wafer is polished with a polishing machineusing a carrier to hold the silicon wafer, wear on the carrier causes adeformation of the carrier itself. As a result, the polishing accuracy(specifically, evenness, flatness, roughness, parallelism/thicknessvariation, etc.) is reduced. However, according to the method forpolishing a silicon wafer according to the present invention and thepolishing liquid according to the present invention, as described above,wear on the carrier exposed to the polishing together with the polishingof the silicon wafer can be reduced while maintaining a good polishingrate for polishing the silicon wafer. Thus, the decrease of the abovepolishing accuracy due to a deformation of the carrier itself can besuppressed. Namely, according to the method for polishing a siliconwafer according to the present invention and the polishing liquidaccording to the present invention, the improvement of the polishingaccuracy of a silicon wafer can be made possible.

Furthermore, according to the method for polishing a silicon waferaccording to the present invention and the polishing liquid according tothe present invention, when polishing a silicon wafer with a polishingmachine using a carrier to hold the silicon wafer, the amount of wear ofthe carrier can be reduced. Thus, the reduction of a frequency ofcarrier replacement, the suppression of variation in polishing rate andpolishing quality, and reduction of noise (abnormal noise) generatedfrom the carrier worn by polishing can be provided.

Therefore, according to the method for polishing a silicon waferaccording to the present invention and the polishing liquid according tothe present invention, when polishing a silicon wafer with a polishingmachine using a carrier to hold the silicon wafer, polishing accuracy ofa silicon wafer can be simply and efficiently improved, and productivitycan be further improved, compared with the cases of using, whenpolishing a silicon wafer with the same polishing machine, theconventional polishing method and the conventional polishing liquid.

In the present invention, as one aspect thereof, for example, by using apolishing liquid that includes silica particles at a silicaconcentration of 0.1% by mass to 5% by mass, which have an averageprimary particle size in the range of 4 nm to 30 nm as measured by BETmethod in the polishing liquid, wear on a carrier can be reduced, andthe improvement of the polishing accuracy when polishing a silicon wafercan be made possible.

DESCRIPTION OF EMBODIMENTS

Examples of the “polishing machine using a carrier to hold a siliconwafer” used in the present invention include a single-sided polishingmachine and a double-sided polishing machine. Among them, thedouble-sided polishing machine is preferable in that many silicon waferscan be processed at the same time by a processing method referred to asa batch treatment. However, the polishing machine using a carrier tohold a silicon wafer is not particularly limited as long as the objectsof the present invention can be achieved.

It is preferable that the “polishing liquid” used in the presentinvention includes silica particles consisting of: silica particleshaving an average primary particle size of 4 nm to 30 nm (i.e., 4 nm ormore and 30 nm or less) as measured by the BET method (in the presentapplication, these particles are referred to as “silica particles (A)”);and silica particles having an average primary particle size of morethan 30 nm and 50 nm or less as measured by the BET method (in thepresent application, these particles are referred to as “silicaparticles (B)”), wherein a mass ratio of the silica particles (A) to thesilica particles (B) is in the range of 100:0 to 85:15 in a notation ofthe silica particles (A):the silica particles (B) (i.e., 100:0 or moreand 85:15 or less). Here, “the silica particles (A):the silica particles(B) is 100:0” means that the silica particles (i.e., the silicaparticles consisting of the silica particles (A) and the silicaparticles (B)) consist only of the silica particles (A) having anaverage primary particle size in the range of 4 nm to 30 nm as measuredby the BET method.

Furthermore, the concentration of the silica in the above “polishingliquid” (i.e., the silica particles consisting of the silica particles(A) and the silica particles (B), and having a mass ratio of the silicaparticles (A) to the silica particles (B) of 100:0 to 85:15 in anotation of the silica particles (A):the silica particles (B)) ispreferably 0.1% by mass to 5% by mass (i.e., 0.1% by mass or more and 5%by mass or less). The upper limit is more preferably 3.5% by mass, evenmore preferably 2.5% by mass, and further preferably 2.0% by mass.

The above silica particles (specifically, the silica particles (A) andthe silica particles (B)) are silica particles derived from an aqueoussilica sol, and an alkaline component, a water-soluble compound, and achelating agent may be optionally added to the silica sol, therebyproducing a polishing liquid.

Although these silica particles are spherical silica particles, theshapes thereof are not a perfect sphere, and by using these silicaparticles, the improvement of the polishing rate of a silicon wafer andthe reduction of wear on a carrier can be provided.

The average primary particle size of the silica particles (specifically,each average particle size of the silica particles (A) and the silicaparticles (B)) can be expressed as a sphere-equivalent particle sizecalculated from the surface area obtained by a nitrogen gas adsorptionmethod (i.e., BET method).

As described above, in the present invention, it is preferable that thepolishing liquid includes silica particles consisting of the silicaparticles (A) having an average primary particle size of 4 nm to 30 nmas measured by the BET method and the silica particles (B) having anaverage primary particle size of more than 30 nm and 50 nm or less asmeasured by the BET method, wherein a mass ratio of the silica particles(A) to the silica particles (B) is 100:0 to 85:15. In the presentinvention, the silica particles (A) can be included as the maincomponent, and the silica particles (B) can be included in the aboveratio.

Also, in the present invention, it is preferable that both the silicaparticles (A) and the silica particles (B), used in the above “polishingliquid” have a ratio (X2/X1) in the range of 1.2 to 1.8 (i.e., 1.2 ormore and 1.8 or less) when representing a major-axis average particlesize calculated from projection images by transmission electronmicroscope (i.e., transmission electron microscope) as (X2) nm and asphere-equivalent particle size calculated from the surface area (orspecific surface area) as measured by the BET method as an averageprimary particle size (X1) nm. Namely, as for the silica particles (A),it is preferable that the ratio (X2/X1) is 1.2 to 1.8 when representinga major-axis average particle size calculated from projection images bytransmission electron microscope as (X2) nm and an average primaryparticle size as measured by the BET method as (X1) nm. As for thesilica particles (B), it is also preferable that the ratio (X2/X1) is1.2 to 1.8 when representing a major-axis average particle sizecalculated from projection images by transmission electron microscope as(X2) nm and an average primary particle size as measured by the BETmethod as (X1) nm.

The case where the silica particles (A):the silica particles (B) is100:0 means that it is preferable that only the silica particles (A)satisfy the ratio (X2/X1) in the above range.

Furthermore, as silica particles used in the present invention, thesilica particles in which a ratio of a major-axis average particle size(X2) nm calculated from projection images by transmission electronmicroscope (i.e., transmission electron microscope) to asphere-equivalent particle size (X1) nm calculated from the surfacearea, namely, X2/X1 is in the range of 1.2 to 1.8 can be used.

Specifically, in the present invention, it is preferable that both thesilica particles (A) and the silica particles (B), used in the above“polishing liquid” have a ratio (X2/X1) in the range of 1.2 to 1.8(i.e., 1.2 or more and 1.8 or less) when representing a major-axisaverage particle size calculated from projection images by transmissionelectron microscope (i.e., transmission electron microscope) as (X2) nmand a sphere-equivalent particle size calculated from the surface area(or specific surface area) as measured by the BET method as an averageprimary particle size (X1) nm. Namely, as for the silica particles (A),it is preferable that the ratio (X2/X1) is 1.2 to 1.8 when representinga major-axis average particle size calculated from projection images bytransmission electron microscope as (X2) nm and an average primaryparticle size as measured by the BET method as (X1) nm. As for thesilica particles (B), it is also preferable that the ratio (X2/X1) is1.2 to 1.8 when representing a major-axis average particle sizecalculated from projection images by transmission electron microscope as(X2) nm and an average primary particle size as measured by the BETmethod as (X1) nm.

The case where the silica particles (A):the silica particles (B) is100:0 means that it is preferable that only the silica particles (A)satisfy the ratio (X2/X1) in the above range.

Both X2 and X1 are average particle sizes as described above. Forexample, X2 can be determined by arbitrarily selecting 100 particles ina transmission electron micrograph, measuring the major axis of eachparticle, and calculating their average value. X1 is a sphere-equivalentparticle size calculated from the surface area, and can be used as avalue of an average primary particle size as measured by the BET method.

As described above, the polishing liquid includes silica particlesconsisting of the silica particles (A) and the silica particles (B) inthe range of 100:0 to 85:15 in the notation of the silica particles(A):the silica particles (B), and the silica concentration is preferably0.1% by mass to 5% by mass (the upper limit thereof is more preferably2.5% by mass and further preferably 2.0% by mass). However, instead ofthe polishing liquid, a polishing liquid including silica particlesconsisting only of silica particles having an average primary particlesize of more than 30 nm and less than 45 nm as measured by the BETmethod at a silica concentration of 0.1% by mass or more and less than2.5% by mass may be used.

In the present application, when the silica particles included in thepolishing liquid consist only of silica particles having an averageparticle size of more than 30 nm and less than 45 nm as measured by theBET method, for convenience, the silica particles are also referred toas “silica particles (B′)” in order to distinguish them from the “silicaparticles (B)” including the average particle size of more than 30 nmand less than 45 nm.

When the silica particles included in the polishing liquid are silicaparticles (B′) (i.e., the silica particles included in the polishingliquid consist only of the silica particles having an average primaryparticle size of more than 30 nm and less than 45 nm as measured by theBET method), and the silica concentration is preferably 0.1% by mass ormore and less than 2.5% by mass, more preferably 0.1% by mass or moreand 1.0% by mass or less, and further preferably 1.0% by mass.

When the silica particles in the polishing liquid consist only of thesilica particles (A), the present invention is a method for polishing asilicon wafer by a polishing machine using a carrier to hold the siliconwafer, wherein the polishing liquid used in the polishing machineincludes the silica particles (A) having an average primary particlesize of 4 nm to 30 nm as measured by the BET method, and in the method,the polishing liquid having a silica concentration of 0.1% by mass to 5%by mass, more preferably 0.1% by mass to 3.5% by mass, even morepreferably 0.1% by mass to 2.5% by mass, still more preferably 0.1% bymass to 2.0% by mass is used.

When the silica particles in the polishing liquid consist of the silicaparticles (A) and the silica particles (B), wherein the silica particles(A): the silica particles (B) are in the range of 100:0 to 85:15, andthe silica concentration is 0.1% by mass to 5% by mass, it is preferablethat both the silica particles (A) and the silica particles (B) used inthe “polishing liquid” have a ratio (X2/X1) in the range of 1.2 to 1.8when representing a major-axis average particle size calculated fromprojection images by transmission electron microscope (i.e.,transmission electron microscope) as (X2) nm and a sphere-equivalentparticle size calculated from the surface area (or specific surfacearea) as measured by the BET method as an average primary particle size(X1) nm.

When the silica particles in the polishing liquid are silica particles(B′), wherein the silica concentration is 0.1% by mass or more and lessthan 2.5% by mass, it is preferable that the silica particles (B′) hasthe range of 1.2 to 1.8 as (X2/X1) obtained in the same way as thesilica particles (A) and the silica particles (B).

In the present invention, the polishing can be performed using asingle-sided polishing machine under a load of 30 to 1000 g/cm² (i.e.,30 g/cm² or more and 1000 g/cm² or less) and under the conditions of asurface plate rotation speed of 10 to 300 rpm (i.e., 10 rpm or more and300 rpm or less), a polishing time of 1 to 30 hours (i.e., 1 hour ormore and 30 hours or less), and a polishing liquid supply amount of 10to 400 ml/min (i.e., 10 ml/min or more and 400 ml/min or less).Preferably, the polishing is performed using a double-sided polishingmachine under a load of 30 to 1000 g/cm² (i.e., 30 g/cm² or more and1000 g/cm² or less) and under the conditions of lower surface platerotation speed of 5 to 100 rpm (i.e., 5 rpm or more and 100 rpm orless), an upper surface plate rotation speed of 2 to 30 rpm (i.e., 2 rpmor more and 30 rpm or less), a lower surface plate/upper surface platerotation ratio of 1 to 10 (i.e., one or more and 10 or less), apolishing time 10 minutes to 3 hours (i.e., 10 minutes or more and 3hours or less), a polishing liquid supply amount of 1 to 20liters/minute (i.e., 1 liter/minute or more and 20 liters/minute orless).

Examples of the carrier used in the present invention include a glassepoxy (in the present application, it is also referred to as an “epoxyglass”) resin carrier, a vinyl chloride resin carrier, a carbon carrier,and a polycarbonate resin carrier.

The above carrier can have a coating structure, wherein the surfacethereof is coated with a hard resin. Examples of the hard resin includea hard material selected from the group consisting of polyvinylidenefluoride, polyamide, polypropylene, polyethylene, polyethyleneterephthalate, polycarbonate, polystyrene, and a polymer alloy thereof.

An epoxy glass carrier of which the thickness is arbitrarily set can beused in consideration of the thickness of a wafer. The glass epoxy resincarrier which is often used as a carrier and is less likely to warp andimproves plate thickness accuracy can be applied. A laminated boardusing the glass epoxy resin is a laminated board made of a thermosettingresin produced by stacking two or more layers of sheets in which a glassfiber is impregnated with an epoxy resin, heating and pressurizing them.

The polishing liquid used in the present invention can be produced basedon an aqueous silica sol. For example, the aqueous silica sol can beobtained by growing, under heating, particles of an active silicic acidobtained by a cation exchange of water glass. As such a silica sol, forexample, SNOWTEX (trade name) manufactured by Nissan ChemicalCorporation can be used.

At least one additive agent selected from the group consisting of an“alkaline component”, a “water-soluble compound” that can be in the formof a water-soluble resin, and a “chelating agent” that can be in theform of a chelating resin can be added to the silica sol to prepare thepolishing liquid.

As the “alkaline component”, sodium hydroxide, potassium hydroxide,ammonia, primary ammonium hydroxide, secondary ammonium hydroxide,tertiary ammonium hydroxide, quaternary ammonium hydroxide (for example,ethyltrimethylammonium hydroxide (ETMAH)), lithium carbonate, sodiumcarbonate, potassium carbonate, lithium hydrogen carbonate, sodiumhydrogen carbonate, potassium hydrogen carbonate, sodium hydroxide, orpotassium hydroxide can be used.

By adding the alkaline components to the silica sol, a pH value of thepolishing liquid can be adjusted in the range of 7 to 12 (i.e., 7 ormore and 12 or less).

As the “chelating agent”, an aminocarboxylic acid-based chelating agent(for example, ethylenediaminetetraacetate sodium (EDTA)) or a phosphonicacid-based chelating agent can be used.

As the “water-soluble compound”, any water-soluble compound can be used.For example, a hydroxyethyl cellulose, glycerin, a polyglycerin, apolyvinyl alcohol, or a carboxyl group- or sulfonic acid group-modifiedpolyvinyl alcohol can be used.

The present invention relates to a method of making wear on a carrierreduced in a method for polishing a silicon wafer with a polishingmachine using a carrier to hold the silicon wafer. The amount of wear ofa carrier is arbitrarily determined depending on the conditions for use.In the present invention, considering the relation with polishingaccuracy, for example, the case where the amount of wear on one side ofthe carrier is within 3 μm when the polishing is continuously performedfor 8 hours can be defined as preferable because the amount of wear islow. The amount of wear is more preferably in the range of 1.9 μm orless, and further preferably in the range of 1.8 μm or less.

Next, the present invention is described in detail with reference tospecific examples, but the present invention is not limited to theseexamples.

EXAMPLES

A commercially available silicon wafer was polished by the followingmethod.

First, various kinds of colloidal silicas were prepared, and variouskinds of polishing compositions were prepared using them. Here, the“colloidal silica” means silica particles included in a silica sol.Next, these various polishing compositions were used as a polishingliquid used in a polishing machine for polishing a silicon wafer using acarrier to hold the silicon wafer, and a commercially available siliconwafer was polished using each of them. An effect of the polishingcomposition that is a specific embodiment of the present invention wasevaluated from the polishing rate and the amount of wear on a carrierafter the polishing was continuously performed for 8 hours. The detailsare shown below.

1) Preparation of Polishing Composition (i.e., Polishing Liquid)

First, the following colloidal silicas A to G were prepared.

Colloidal silica A: Colloidal silica with average primary particle sizeof 23 nm determined by nitrogen gas adsorption method (i.e., BET method)(silica particles based on silica sol, ratio (X2/X1) is 1.4).

Colloidal silica B: Colloidal silica with average primary particle sizeof 25 nm determined by nitrogen gas adsorption method (i.e., BET method)(silica particles based on silica sol, ratio (X2/X1) is 1.4).

Colloidal silica C: Colloidal silica with average primary particle sizeof 21 nm determined by nitrogen gas adsorption method (i.e., BET method)(silica particles based on silica sol, ratio (X2/X1) is 1.7).

Colloidal silica D: Colloidal silica with average primary particle sizeof 45 nm determined by nitrogen gas adsorption method (i.e., BET method)(silica particles based on silica sol. (X2/X1) ratio is 1.2).

Colloidal silica E: Colloidal silica with average primary particle sizeof 35 nm determined by nitrogen gas adsorption method (i.e., BET method)(silica particles based on silica sol, ratio (X2/X1) is 1.3).

Colloidal silica F: Colloidal silica with average primary particle sizeof 60 nm determined by a nitrogen gas adsorption method (i.e., BETmethod) (silica particles based on silica sol, ratio (X2/X1) is 1.2).

Colloidal silica G: Colloidal silica with average primary particle sizeof 20 nm determined by nitrogen gas adsorption method (i.e., BET method)(silica particles based on silica sol, ratio (X2/X1) is 1.9).

An aqueous silica sol that was commercially available (manufactured byNissan Chemical Corporation, trade name: SNOWTEX) was used for thepreparation of each colloidal silica above. Each silica sol can beproduced by particle growth of an active silicic acid obtained by acation exchange of water glass under heating.

In the “ratio (X2/X1)” that specifies the silica particles of eachcolloidal silica above, X1 represents an average primary particle size(nm) determined by the nitrogen gas adsorption method (i.e., BETmethod), and X2 represents a major-axis average particle size (nm)calculated from a transmission projection image obtained using anelectron beam.

The X1 is defined as the sphere-equivalent particle size (nm) calculatedfrom the surface area (or specific surface area) measured using thenitrogen gas adsorption method (i.e., BET method) as the average primaryparticle size (in the present application, the average primary particlesize is also referred to as “(X1) nm”). Specifically, as for each of theabove colloidal silicas, the specific surface area S (m²/g) of thesilica particles is measured using a BET specific surface area analyzer(Monosorb manufactured by Quantachrome Instruments Japan G. K.), andfrom the specific surface area S (m²/g) measured by the nitrogenadsorption method as a sphere-equivalent size, the sphere-equivalentparticle size ((X1) nm) was calculated using the formula: “((X1)nm)=2720/S”, and this calculated value was defined as the averageprimary particle size ((X1) nm) as measured by the BET method.

The X2 value is the major-axis average particle size (nm) calculatedfrom a transmission projection image obtained using an electron beam (inthe present application, the average particle size is also referred toas “(X2) nm”). Specifically, the transmission electron microscope whichis referred to as “H8000” (trade name) manufactured by HitachiHigh-Technologies Corporation was used. And, from the transmissionelectron micrograph of the silica particles of each colloidal silicaabove, obtained using this microscope, 100 particles were arbitrarilyselected. Then, the major axis of each particle was measured, and theaverage of them was defined as the major-axis average particle size.

Next, polishing compositions (1) to (8) and comparative polishingcompositions (1) to (7) for comparison with them were produced bycontaining each colloidal silica above, an alkaline component, and achelating agent at the ratio as shown in the tables below, and thus theremaining component in each composition shown in the tables is water.The produced polishing compositions (1) to (8) and comparative polishingcompositions (1) to (7) were used as polishing liquids as describedbelow.

Ethyltrimethylammonium hydroxide (ETMAH) was used as the alkalinecomponent, and sodium ethylenediaminetetraacetate (EDTA) was used as thechelating agent. Reagents were used as these components. ETMAH which wascommercially available was used, and EDTA manufactured by CHELESTCORPORATION was used.

To all polishing compositions 1000 ppm of potassium carbonate was addedas a pH buffer.

In addition, the “Ratio: % by mass” described together with “Kinds ofsilica” in the tables indicates the blending ratio of each colloidalsilica of the sources of the silica particles in the polishingcomposition in units of % by mass. For example, the description in thepolishing composition (1) means that the colloidal silica used in theproduction of its composition is only colloidal silica A, and thedescription in the polishing composition (6) means that the colloidalsilica used in the production of its composition consists of thecolloidal silica A and the colloidal silica D, and further the massratio of the two, namely, the colloidal silica A:the colloidal silica D,is 90:10.

TABLE 1 Polishing Silica Kinds of silica Additive amount of Additiveamount of composition No. pH concentration (Ratio: % by mass) alkalinecomponent chelating agent (1) 10.6 1.0% by mass Colloidal silica A(100%) 500 ppm 200 ppm (2) 10.6 2.5% by mass Colloidal silica A (100%)500 ppm 200 ppm (3) 10.5 3.5% by mass Colloidal silica A (100%) 500 ppm200 ppm (4) 10.7 1.0% by mass Colloidal silica B (100%) 500 ppm 200 ppm(5) 11.0 1.0% by mass Colloidal silica C (100%) 500 ppm 200 ppm (6) 10.71.0% by mass Colloidal silica A (90%) + 500 ppm 200 ppm Colloidal silicaD (10%) (7) 10.6 2.5% by mass Colloidal silica A (90%) + 500 ppm 200 ppmColloidal silica D (10%) (8) 11.0 1.0% by mass Colloidal silica E (100%)500 ppm 200 ppm

TABLE 2 Comparative polishing Silica Kinds of silica Additive amount ofAdditive amount of composition No. pH concentration (Ratio: % by mass)alkaline component chelating agent (1) 10.7 2.5% by mass Colloidalsilica E (100%) 500 ppm 200 ppm (2) 10.7 1.0% by mass Colloidal silica D(100%) 500 ppm 200 ppm (3) 11.2 1.0% by mass Colloidal silica F (100%)500 ppm 200 ppm (4) 10.6 1.0% by mass Colloidal silica A (80%) + 500 ppm200 ppm Colloidal silica D (20%) (5) 10.6 2.5% by mass Colloidal silicaA (80%) + 500 ppm 200 ppm Colloidal silica D (20%) (6) 10.6 7.0% by massColloidal silica A (100%) 500 ppm 200 ppm (7) 10.7 1.0% by massColloidal silica G (100%) 500 ppm 200 ppm

2) Polishing Method and Results

The above polishing compositions (the polishing compositions (1) to (8)and the comparative polishing compositions (1) to (7)) were used as thepolishing liquid used in a polishing machine for polishing a siliconwafer using a carrier to hold the silicon wafer, and a silicon waferwhich was commercially available was polished. The polishing conditionsin this case are shown below.

2-1) Polishing Conditions

Polishing machine: Double-sided polishing machine 13BF manufactured byHAMAI CO., LTD,

Load: 150 g/cm²,

Upper surface plate rotation speed: 7 rpm,

Lower surface plate rotation speed: 20 rpm,

Rotation ratio: three,

Carrier rotation number: 5.9 rpm, carrier revolution number: 6.6 rpm,and carrier rotation direction: clockwise rotation,

Polishing pad: Polishing pad made of a foamed polyurethane (LP-57(groove width: 2 mm, groove pitch: 20 mm)),

Supply amount of polishing liquid: 6.0 L/min,

Polishing temperature: 25° C.,

Number of polished sheets: three wafers per one carrier,

Carrier: Epoxy glass carrier (thickness: 0.70 mm),

Polishing time for continuously polishing multiple silicon wafers: 8hours,

Silicon wafer: size: 200 mm; conduction type: P type; crystalorientation: <100>; resistivity: less than 100 Ω·cm.

2-2) Polishing Results

A table below shows the polishing results when polishing under the abovepolishing conditions. The amount of wear on a carrier in the table isthe amount of wear on one side of the carrier after the polishing wascontinuously polished for 8 hours.

TABLE 3 Polishing Amount of wear on Polishing rate of composition No.carrier (μm/8 hours) wafer (μm/min) (1) 0.0 0.28 (2) 0.6 0.29 (3) 1.50.29 (4) 1.2 0.25 (5) 0.0 0.25 (6) 0.1 0.27 (7) 1.8 0.29 (8) 1.9 0.25

TABLE 4 Comparative polishing Amount of wear on Polishing rate ofcomposition No. carrier (μm/8 hours) wafer (μm/min) (1) 10.5 0.27 (2)5.6 0.26 (3) 4.2 0.24 (4) 5.8 0.27 (5) 6.5 0.29 (6) 5.6 0.26 (7) 5.30.28

For example, comparing the above results between the polishingcomposition (3) and the comparative polishing composition (7), whenpolishing a silicon wafer with a polishing machine using a carrier tohold the silicon wafer, in the case of using a polishing liquidincluding silica particles at a silica concentration in the range of0.1% by mass to 5% by mass, wherein the silica particles consist of thesilica particles (A) having an average primary particle size of 4 nm to30 nm as measured by the BET method, and having a ratio (X2/X1) in therange of 1.2 to 1.8, it has been confirmed that while maintaining a goodpolishing rate in the range of 0.25 to 0.29 μm/min, the amount of wearon one side of the carrier can be suppressed to an extremely good valueof 1.5 μm/8 hours which is less than 1.8 μm/8 hours after the polishingwas continuously performed for 8 hours.

Furthermore, for example, comparing the above results between thepolishing compositions (1) to (3) and the comparative polishingcomposition (6), when polishing a silicon wafer with a polishing machineusing a carrier to hold the silicon wafer, in the case of using apolishing liquid including silica particles at a silica concentration inthe range of 0.1% by mass to 5% by mass, wherein the silica particlesconsist only of silica particles (i.e., the silica particles (A)) havingan average primary particle size of 4 nm to 30 nm as measured by the BETmethod, it has been confirmed that while maintaining a good polishingrate of 0.25 to 0.29 μm/min, the amount of wear on one side of thecarrier can be suppressed to an extremely good value of not greater than1.5 μm/8 hours which is less than 1.8 μm/8 hours, after the polishing iscontinuously performed for 8 hours.

Furthermore, for example, comparing the above results between thepolishing compositions (6) and (7) and the comparative polishingcompositions (4) and (5), when polishing a silicon wafer with apolishing machine using a carrier to hold the silicon wafer, in the caseof using a polishing liquid including silica particles at a silicaconcentration of 0.1% by mass to 5% by mass, wherein the silicaparticles consist of: silica particles (i.e., the silica particles (A))having an average primary particle size of 4 nm to 30 nm as measured byBET method; and silica particles (i.e., silica particles (B)) having anaverage primary particle size of more than 30 nm and 50 nm or less asmeasured by the BET method, wherein a mass ratio of the two (i.e., thesilica particles (A)/the silica particles (B)) is not less than 85/15,it has been confirmed that while maintaining a good polishing rate inthe range of 0.25 to 0.29 μm/min, the amount of wear on one side of thecarrier can be suppressed to an extremely good value of not greater than1.8 μm/8 hours after the polishing was performed for 8 hours.

Furthermore, comparing the above results between the polishingcomposition (8) and the comparative polishing composition (1), whenpolishing a silicon wafer with a polishing machine using a carrier tohold the silicon wafer, in the case of using a polishing liquidincluding silica particles at a silica concentration in the range of0.1% by mass or more and less than 2.5%, wherein the silica particlesconsist only of silica particles (silica particles (B′)) having anaverage primary particle size of more than 30 nm and less than 45 nm asmeasured by the BET method, it has been confirmed that while maintaininga good polishing rate of 0.25 to 0.29 μm/min, the amount of wear on oneside of the carrier can be suppressed to a good value of not greaterthan 1.9 μm/8 hours, after the polishing was performed for 8 hours.

Therefore, according to the present invention, it has been found thatthe reduction of wear (i.e., wear prevention) on a carrier can be madepossible while maintaining a good polishing rate. As a result, it wasfound that the present invention is excellent in terms of extending thereplacement period of a carrier and accuracy of the polished surface ofthe obtained wafer.

INDUSTRIAL APPLICABILITY

The present invention provides, in a method for polishing a siliconwafer with a polishing machine using a carrier to hold the siliconwafer, a method of making wear on a carrier reduced, and further makingnoise generated from the carrier reduced.

According to the present invention, when polishing a silicon wafer witha polishing machine using a carrier to hold the silicon wafer, apolishing method capable of: reducing wear on the carrier whilemaintaining a good polishing rate; improving polishing accuracy;reducing the frequency of carrier replacement; suppressing variations inpolishing rate and polishing quality can be suppressed; and reducingnoise (i.e., abnormal noise) generated from carriers can be provided,and thus the present invention has the applicability in variousindustrial fields (particularly, in fields such as a highly reliablesemiconductor device and electronic component device) that are desiredto easily and efficiently improve polishing accuracy of a silicon waferby using a carrier.

1. A polishing liquid for a polishing machine using a carrier to hold asilicon wafer, the polishing liquid comprising silica particles at asilica concentration of 0.1% by mass to 5% by mass, the silica particlesconsisting of: silica particles (A) having an average primary particlesize of 4 nm to 30 nm as measured by BET method, and having a ratio(X2/X1) of 1.2 to 1.8 when representing a major-axis average particlesize calculated from projection images by transmission electronmicroscope as (X2) nm and an average primary particle size as measuredby the BET method as (X1) nm; and silica particles (B) having an averageprimary particle size of more than 30 nm and 50 nm or less as measuredby the BET method, and having a ratio (X2/X1) of 1.2 to 1.8 whenrepresenting a major-axis average particle size calculated fromprojection images by transmission electron microscope as (X2) nm and anaverage primary particle size as measured by the BET method as (X1) nm,wherein a mass ratio of the silica particles (A) to the silica particles(B) is 100:0 to 85:15.
 2. A polishing liquid for a polishing machineusing a carrier to hold a silicon wafer, the polishing liquidcomprising: silica particles at a silica concentration of 0.1% by massto 5% by mass, the silica particles consisting of: silica particles (A)having an average primary particle size of 4 nm to 30 nm as measured byBET method, and silica particles (B) having an average primary particlesize of more than 30 nm and 50 nm or less as measured by the BET method,wherein a mass ratio of the silica particles (A) to the silica particles(B) is 100:0 to 85:15; or silica particles at a silica concentration of0.1% by mass or more and less than 2.5% by mass, the silica particlesconsisting only of silica particles (B′) having an average primaryparticle size of more than 30 nm and less than 45 nm as measured by theBET method.
 3. The polishing liquid according to claim 2, wherein thesilica particles (A), the silica particles (B), and (B′) have, whenrepresenting a major-axis average particle size calculated fromprojection images by transmission electron microscope as (X2) nm and anaverage primary particle size as measured by the BET method as (X1) nm,a ratio (X2/X1) of 1.2 to 1.8.